Comparative Evaluation of the Vector Competence of Four South American Populations of the Rhipicephalus sanguineus Group for the Bacterium Ehrlichia canis, the Agent of Canine Monocytic Ehrlichiosis

Abstract

This study compared the vector competence of four populations of Rhipicephalus sanguineus group ticks for the bacterium Ehrlichia canis, the agent of canine monocytic ehrlichiosis (CME). Ticks (larvae and nymphs) from the four populations—one from São Paulo state, southeastern Brazil (BSP), one from Rio Grande do Sul state, southern Brazil (BRS), one from Argentina (ARG), and one from Uruguay (URU)–were exposed to E. canis infection by feeding on dogs that were experimentally infected with E. canis. Engorged ticks (larvae and nymphs) were allowed to molt to nymphs and adults, respectively, which were tested by molecular analysis (E. canis-specific PCR assay) and used to infest naïve dogs. Through infestation of adult ticks on naïve dogs, after nymphal acquisition feeding on E. canis-infected dogs, only the BSP population was shown to be competent vectors of E. canis, i.e., only the dogs infested with BSP adult ticks developed clinical illness, seroconverted to E. canis, and yielded E. canis DNA by PCR. This result, demonstrated by two independent replications, is congruent with epidemiological data, since BSP ticks were derived from São Paulo state, Brazil, where CME is highly endemic. On the other hand, BRS, ARG, and URU ticks were derived from a geographical region (South America southern cone) where CME has never been properly documented. Molecular analysis of unfed adults at 30 days post molting support these transmission results, since none of the BRS, ARG, and URU ticks were PCR positive, whereas 1% of the BSP nymphs and 31.8% of the BSP adults contained E. canis DNA. We conclude that the absence or scarcity of cases of CME due to E. canis in the South America southern cone is a result of vector incompetence of the R. sanguineus group ticks that prevail on dogs in this part of South America.

Survey of spatial distribution of vector-borne disease in neighborhood dogs in southern Brazil

“…In Brazil, previous studies have shown that the prevalence of CVBDs in dogs in urban areas has varied from absence to 91.2% (Lasta et al, 2013;Spolidorio et al, 2013;Vieira et al, 2013b). Although the neighborhood dogs of the present study had comparatively lower CVBD prevalence (Vieira et al, 2013b;Azzag et al, 2015), the wide differences in CVBD prevalence may be explained by the populations studied, lifestyles, environmental occurrence of vectors and diseases, diagnostic tests used and vector competence of ticks from the Rhipicephalus sanguineus group (Balakrishnan et al, 2014;Maia et al, 2015;Moraes-Filho et al, 2015). As observed here, infection by CVBDs may occur in the absence of clinical signs (Joppert et al, 2001;Maggi et al, 2014;Azzag et al, 2015) or hematological changes (Novacco et al, 2010;Balakrishnan et al, 2014;Moraes-Filho et al, 2015).…”

“…Although the neighborhood dogs of the present study had comparatively lower CVBD prevalence (Vieira et al, 2013b;Azzag et al, 2015), the wide differences in CVBD prevalence may be explained by the populations studied, lifestyles, environmental occurrence of vectors and diseases, diagnostic tests used and vector competence of ticks from the Rhipicephalus sanguineus group (Balakrishnan et al, 2014;Maia et al, 2015;Moraes-Filho et al, 2015). As observed here, infection by CVBDs may occur in the absence of clinical signs (Joppert et al, 2001;Maggi et al, 2014;Azzag et al, 2015) or hematological changes (Novacco et al, 2010;Balakrishnan et al, 2014;Moraes-Filho et al, 2015). A previous study on owned dogs did not show any significant associations between hemoplasma infection and anemia, ectoparasite infestation, gender and clinical status (Tennant et al, 2011), thus corroborating the findings from the neighborhood dogs of the present study.…”

Comparación y utilidad de las regiones mitocondriales de los genes 16S y COX1 para los análisis genéticos en garrapatas (Acari: Ixodidae)

“…ellas (33,34). En los últimos años se ha reconocido la existencia de múltiples complejos de especies en Latinoamérica y el papel que pueden tener algunos de ellos en la diná-mica epidemiológica de enfermedades de interés médico y veterinario en la región (3,4,7,8,10,11). Ante este panorama, los análisis genéticos de las garrapatas pueden proveer información relevante para el estudio y la vigilancia de las enfermedades transmitidas por garrapatas en nuestro país.…”

“…Entre las garrapatas más conocidas se encuentran las de la especie Rhipicephalus microplus, las cuales ocasionan enormes pérdidas económicas por los daños directos e indirectos que ocasiona en el ganado bovino (2). También están las garrapatas del complejo R. sanguineus, vectores de la erliquiosis y la trombocitopenia cíclica infecciosa en caninos (3,4), que también pueden transmitir enfermedades a los humanos, como la fiebre botonosa mediterránea (2) y la fiebre manchada de las Montañas Rocosas (5).…”

“…Entre los ejemplos más notables de ajustes taxonómicos en los que los análisis genéticos han sido definitivos en la descripción de nuevas especies y en la identificación de complejos en las familias Ixodidae y Argasidae, están el complejo Rhipicephalus sanguineus (6)(7)(8), el grupo Ornithodoros talaje (9) y el complejo Amblyomma cajennense (10,11). Debido a las peculiaridades biológicas y ecológicas que presentan las diferentes especies y grupos de especies de garrapatas, los estudios genéticos se han convertido en una herramienta importante para explorar las relaciones poblaciones (8,(12)(13)(14), delimitar las especies (15)(16)(17), hacer los análisis filogenéticos (18)(19)(20), e, incluso, identificar potenciales zonas de riesgo de transmisión de enfermedades (3,7,8).…”